The present invention relates to a method for producing a controllable and reproducible temperature in a pre-determined direction of heat-conducting plates for the separation of mixtures of substances in sheet-shaped separating media. Furthermore, the invention relates to a device for producing such a temperature gradient and to its use for the separation of substance mixtures, wherein at least one component undergoes a thermal conversion within the temperature range of temperature gradient.
It has been known that a number to naturally occurring substances having higher molecular weights undergo conversions or irreversible changes at increasing temperatures and that these changes may be analytically evaluated. D. R. Thatcher and B. Hodson, in Biochem. (1981) 197, pp. 105-109, investigated the denaturation of proteins and nucleic acids by means of the application of a thermal gradient during electrophoresis and observed that thermally caused changes can be rendered visible thereby. For producing a temperature gradient they designed an apparatus which could be positioned on both sides of a vertical polyacrylamide gel plate, whereupon thermostatically controlled water at different temperatures is passed through both ends of the aluminum plates. The two plates were connected to each other in series and it was assumed that an identical thermal gradient thereby was formed. However, there are disadvantages to this device, in that it is not only complicated in design and difficult to handle, but also suffers from a basic error since a controllable and reproducible temperature gradient cannot be established. An undesired and interfering temperature gradient was formed between the inlet and outlet of the water bath by the flow through the two plates connected in series. This in turn leads to an occurrence of different temperatures and non-parallel temperature gradients in the two plates. This results in the gel electrophoresis plate having different temperatures at its front and back surfaces.